6. Influence of capture method on quality and possible survival

Fishing methods will influence the quality and therefore usefulness of
fish which is discarded. Gillnets, for instance which may be set at sun-down and lifted
again at sun-up may have fish in them which has been dead for a number of hours. In
tropical waters where sea temperatures can be in the mid 20s Celsius fish can be
partially spoilt and may also be attacked by predatory species such as shark. This applies
not only to any potential discards, of course, but also to target fish species. Indeed one
of the reasons for discards at sea can be that target species are already spoilt before
lifting the net.

The quality of trawled fish similarly will depend on time of soaking as
well as such factors as the amount of fish in the cod end, the water temperature, the type
of substrate etc. Kungsawan (1996) asserts that in Thailand, the quality of bycatch from
otter trawl vessels catching shrimp as their main target is worse than that from pair
trawlers or gill netters. This results in most otter trawl bycatch being used for fish
meal, whereas bycatch from other shrimp fishing methods is more likely to be used for
human foods.

The best quality fish at capture will be associated with fishing
methods that remove fish from the water immediately they are caught and where fish are
usually alive at this stage. These would include the various surrounding and lifting nets
and some hook and line fisheries such as pole and line and hand lines. It is usually the
case, for instance, that trawl caught fish will be less valuable than fish of the same
species caught by hand line. Where fish are discarded from this type of fishery there is
also a higher likelihood that they will be discarded alive, that is released, and that
they may survive. The fact that they are released alive does not, of course mean that they
will survive. Damage inflicted by the catching method may mean they will die later or fall
victim to predators or disease because they are in a weakened state. The fact that that
they may be released back into a different location and habitat may also mean that they
have less chance of survival.

Fish caught and likely to be discarded are usually going to be treated
badly so that their quality is not preserved. The possibility of using the fish for human
consumption will normally only be possible if some sort of onboard preservation is used or
the fish is unloaded onto carrier vessels, for instance, for swift movement to shore base
facilities for preservation and processing.